For methods of sensing the conceptive period, known are an Ogino's rhythm method of birth control and a basal bodily temperature method. However, it is troublesome in the former Ogino's method to count a certain period of days, and in the latter method to carefully take the bodily temperatures at determined time for long period of days and keep records of them. In addition, there has never been developed such a menstruation periodic counter of compact size which may indicate functionally values of data obtained from these methods.